Electric motor system for multiple loop controls



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ATTORNEY Frank C. Fenriell J m0 h- 33303. a n. g

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. N a kl (I: O 5 1 e so Lg INVENTORS and John R Erbe BY Mt.

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Filed June 19, 1953 March 8, 1955 F. c. FENNELL ETAL ELECTRIC MOTOR SYSTEM FOR MULTIPLE LOOP CONTROLS 9 9 E 2 5:2 3:223 u nu Q .0 E T O: 0- O D T I'- I 9 a n. a a m -6 u z a E 6 2Q 3 u I I O .1 II -L N5 lllll M llll .5 S

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United States Patent ELECTRIC MOTOR SYSTEM FOR MULTIPLE LOOP CUNTROLS Frank C. Fennell, Greensburg, and John R. Erbe, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvanin Application June 19, 1953, Serial No. 362,808 11 Claims. (Cl. 3l8--7) Our invention relates, generally, to loop control sys terns, and has reference, in particular, to control systems such as may be used for controlling multiple loops of a strip of material in connection with strip processing systems and the like.

Continuous processing lines for processing sheet material usually require storage loops at the entry end and the delivery end of the process zone to permit attaching new coils of material and removing full coils. Where storage requirements are relatively small a single free hanging loop is generally used. When relatively large storage of material is needed multiple loops are required. To control the length of two or more loops a cumbersome mechanical arrangement of counterweighted floating rolls has been commonly used. in some cases photoelectrically controlled apparatus has been used. In either case the control was by a stepby-step method.

On many processing lines, a step-by-step control is not desirable but a continuous or stepless method of correction is needed.

One broad object of our invention is the provision of a stepless, or continuous, control elfect to maintain a plurality of storage loops of sheet material at a constant length.

Another object of our invention is to provide, in a multiple loop control system, for continuously varying the speed of a pinch roll positioned intermediate a pair of freely suspended loops of a strip of material so as to maintain the speed of the strip at the pinch roll at a value half way between the speeds of the strip at pinch rolls preceding and following the loops.

Yet another object of our invention is to provide, in a loop control system, for varying the speed of a motor, connected in driving relation with a strip of material between a pair of loops, in accordance with voltages applied to motors connected in driving relation with the strip ahead of and following said loops.

It is also an object of our invention to provide, in a multiple loop control system, for selectively and continuously varying the speed of a motor, connected with a strip of material between apair of loops, in accordance v with the relative lengths of the loops.

it is an important object of our invention to provide, in a multiple loop control system, for normally maintaining a pair of adjacent loops in a strip of material at substantially the same predetermined length.

Other objects will in part be obvious, and will in part be explained hereinafter.

in accordance with one embodiment of our invention, a strip of material, which is being processed, passes between the rolls of three successive sets of pinch rolls, d1sposed respectively ahead of, between, and following a pair of loops in the material, and is then woundon a reel device. The motors of the first two sets of pinch rolls are energized from a first main generator, while the reel motor and the motor of the last set of pinch rolls are energized from a second main generator. A booster generator is used to vary the voltage applied to the motor of the pinch rolls disposed between the loops, said booster generator having opposing field windings energized in accordance with the voltages of the two mam generators, and which neutralize each other when said voltages are equal. A pair of field windings are provided on the booster generator, and these field windings are connected to photothyratron regulators which have continuously I X 2,703,858 "Patented Mar. s, 1955 variable outputs. The field windings of the pair are wound in opposition and thus operate to equalize the lengths of the loops.

For a more complete understanding of the nature and scope of our invention, reference may be made to the following detailed description, which may be read incon nection with the accompanying drawing, in which:

Figure l is a diagrammatic view of a loop control system showing one embodiment of our invention; and

Fig. 2 is a portion of a diagrammatic view of a loop control system showing a modification of our invention.

Referring to Fig. l, the reference numeral 1 designates the process zone through which the material M is to pass at a constant speed. This constant speed is determined by the pinch rolls 2 and 3 coupled to be driven by the motor A. Motor Ais excited at a selected con" I stant value by its field winding 4.

The speed of motor A is determined by the voltage of generator G1, the voltage of which is determined by adjustment of the excitation of field winding 5 by the motor operated rheostat 6. The position of the rheostat arm of rheostat 6 thus determines the speed of the mate rial M through the processing zone. The material M hangs with a loop Ll between pinch rolls 2 and 3, and the pinch rolls 7 and ii. Pinch rolls 7 and 8 are drivenby motor B, which motor has its field winding 9 excited at a selected value. The speed of motor B is not determined by the voltage of the generator G1 alone but is additionally dependent on the control effect of the buck and boost exciter E. The material M hangs with a free loop L2 between pinch rolls 7 and 8, and Ill and 112 driven by motor C. Motor C has its field winding M excited at a selected constant value and its armature, through the controller Cl, is energized by generator G2.

Generator G2 has two field windings, namely, a control field winding SP3 and the field winding l5 which is energized at any selected value from the terminals shown through the motor operated rheostat 16. The setting of rheostat lie determines the delivery speed of the material.

The rhecstats 6 and 16 may be ganged. But whether ganged or not, the relative setting of the two rheostats should be such that when the exciter E has zero output voltage, when the loops L1 and L2 are at the desired equal lengths, and when there is normal exciting current in the control field winding GT3, as set by the output of LR2 when loop L2 is in the normal position, then metors B and C run at the same speed. The material, after leaving pinch rolls ill. and 12, is wound on the reel core 13 driven by motor D, the armature voltage of which is controlled by the controller C2. The excitation of the field winding 17 is controlled through the regulator 18 and the voltage tapped ed at potentiometer 21 by the lead 19 operated by the dancer roll 20. in brief, the speed of motor D is so changed that the material normally moves onto the reel core at constant linear speed regardless of changes in coil diameter. To provide the necessary tension, motor C normally operates as a drag generator.

The field winding F1 on exciter E is energized as a tunction of the voltage of generator 61. With no excitmg current in any of the other field windings of exciter E this field winding F1 will produce a voltage on exciter E that bucks the voltage of generator 61.

The field winding F3 on exciter E is energized as a function of the voltage of generator G2.

mg current 111 any of the other field windings of exciter that boosts the voltage of generator Gil.

These field windings F1 and F3 thus oppose each other. The two field windings are preferably so designed that, when the voltages of the two generators G1 and G2 are equal, the magnetomotive forces of these two field windings exactly balance each other and the output voltage of exciter E due to these field windings F1 and F3 is zero. Further, each field winding should preferably be so designed that the voltage output of the exciter E for one field winding only is half the voltage applied to the field winding.

For the particular application herein discussed, a con- With no excit siderable material storage is required because the processing in the process zonepontinues at a constant rate but as each' reel becomes full, motors C and D have to be temporarily stopped to remove the full reel, apply the end of the material to a new core and restart the winding core and the pinch rolls 11 and 12. In the main line, the material piles up as loops L1 and L2. When a particular length of strip does not coincide with length on a full reel, which is usually the case, then motors C and D are also stopped long enough to weld the leading end of the following strip to the trailing end-of, the preceding strip. Again, the material piles up as loops L1 and L2. One of the aims, of course, is to maintain the lengths of the loops at equal lengths.

For perfect balance of the two loops the speed of motor B should be one-half the sum of the speeds of motors A and C at all times. Under normal conditions, when the speed of the material passing through the process zone is the same as its delivery speed, the voltage of generator G1 is equal to the voltage of generator G2. In such case, the loops will be balanced and the output voltage of exciter B will be zero, because the effect of field windings F1 and F3 is balanced out. Further, since the loops are at equal lengths and at the desired length, the output of the loop regulators LRl and LR2 will be balanced. namely. the excitation currents in the field windings F5 and F7. being of balanced design and wound in opposition, will be the same.

When the delivery of the material is stopped-for any of the mentioned reasons, or any other reason, motor A is running at full speed and motor C is stopped. Under these conditions, motor B should run at half the speed of. motor A so as to store equal lengths of material in each loop. Under these conditions, the voltage of generator G2 is zero and, for the time being, neglecting the effects of field winding F5 and F7, field winding F1 sup- I plies all the excitation for exciter B. For the desi n characteristics specified for field windings F1 and F3, the voltage of exciter B will be one-half generator G1 and in opposition to the ator G1. Motor B will, therefore, half the speed of motor A.

en the material at the delivery region runs faster than through the process zone in order to pull excess materials out of the loops, the voltage of generator G2 will be higher than the voltage of generator G1. The exciter voltage will thus boost the voltage of generator G1' and is one-half the difference between the voltages of generators G1 and G2. Motor B, therefore, runs at a speed apgrgximately half way between the speeds of motors A an voltage of generrun at approximately It is apparent from the foregoing that under perfect conditions the loops L1 and L2 will be maintained at the same length regardless of the difference in speeds of the process zone and the delivery zone. However, some means is, in practice, necessary to correct an error if and when an error exists.

The ph'otothyratron loop regulators each include an elongated light sensitive device and an elongated source of light L preferably arranged to fall on the respective light sensitive devices in sharp lines. The regulators also include the other elements such regulators are known to include. These photothyratron loop regulators provide a continuous indication of the length of the loops.

The output of the photothyratron regulator LRI is connected to field winding F5 of exciter of loop Ll increases, this field winding F5 produces a voltage on exciter E that boosts the voltage of generator G1.

The output of the photothyratron regulator LR2 is connected to field winding P7 of exciter B. As the length of loop L2 increases, this field winding F7 produces a voltage on exciter E that bucks the voltage of generator G1.

From the foregoing, it is apparent that as long as theloops are of equal length, the output of the loop regulators will be equal and the net effect on exciter B will be zero since the field windings F5 and F7 act in opposition.

If, for example, loop L1 is longer than loop L2, then the voltage output of regulator LRl will be higher than the voltage output of regulator LR2 and the net effect will be to increase the voltage of the exciter E in the sense to boost the voltage of generator G1 to thus increase the speed of motor B until the loops are again of equal lengths.

the voltage of,

- ence characters used in Fig. 1.

. field winding FB is added B. As the length When the delivery section is stopped, the lengths of both loops increases and this excess length of strip must be automatically removed after the delivery section is restarted. This is accomplished by the field winding GF3 connected in series with the output circuit of loop regulator LR2. This field winding GF3 acts to increase the voltage of generator G2 as long as the length of loop L2 is greater than the normal length.

While only two loops have been shown for explanatory purposes, a similar arrangement is applicable with multiple loops by proper design of the uck and boost exciters for the pinch roll motors. Our control is also applicable to loops at difierent positions along the processing line.

An alternate system of control is shown in Fig. 2, where like elements are designated by the same refer- In the control shown in Fig. 2, the required ran e of operation of motor B2, corresponding to motor B, 1s obtained by field control of the motor rather than armature voltage control as shown in Fig. l. The field winding 109of motor B2 is excited by exciter E2, which increases .the excitation on the motor field winding 109 above that supplied from the excitation buses shown. The blocking rectifier R in the armature circuit of exciter E2 prevents the exciter from cancelling out the basic excitation of the buses. The control field windings F1, F3, F5 and F7 on exciter B2 are similar in operation to the same type of field windings on exciter E shown in Fig. 1, with the exception that the senses of the field windings are reversed because the voltage of exciter E2 must be increased in order to slow down the motor speed. In addition, a basic excitation to exciter E2 in order to provide the required motor field voltage when the loops are exactly balanced and the voltages of generators G1 and G2 are matched.

For certain applications, the alternative showing in $31. 2 virill be more economical than the control showing While we have shown one embodiment and but one modification, certain changes and modifications other than those suggested may be made spirit and scope of our invention.

We claim as our invention:

1. In a control system for maintaining a plurality of loops in a moving length of material at equal and constant lengths, in combination, a plurality of motors connected in driving relation with the length of material at spaced apart points ahead of, between and following a pair of loops at the material, generator means connected in series circuit. relation with the motor disposed to operate on the material intermediate the loops and photothyratron loop regulator means having continuous type output as a function of the difference in loop length to effect energization of said motor to run at a speed to produce a strip speed equal to one-half the sum of the speeds of the strip at the other two motors.

2. In a control system for a plurality of motors connected in driving relation with pinch rolls disposed to engage a continuous moving strip of material at points ahead of, between and following a pair of freely suspended loops of said strip, circuit means connecting the motor ahead of and the motor between the loops to a common source of electrical energy, additional circuit means connecting the motor following said loops to another source of electrical energy, and a booster generator connected to vary the voltage applied to the motor between the loops in accordance with a difierential between the voltages of the sources.

3. In a control system for a strip of material having a plurality of freely suspended loops, an entry pinch roll motor connected in driving relation with pinch rolls on the entry side of the loop, an intermediate pinch roll motor connected in driving relation with a pair of pinch rolls intermediate the loops, a main generator connected to supply electrical energy to said motors, a delivery pinch roll motor connected in driving relation with pinch rolls on the delivery side of the loops, an additional main generator connected to supply electrical energy to the delivery pinch roll motor, a booster generator connected in series circuit relation with the intermediate pinch roll motor, said booster generator having a plurality of field windings, circuit means connecting two of said windings one to each of the main and additional main generators in opposed senses, and additional field winding means,

falling within the light sensitive means disposed to be continuously responsive to the difierence in the lengths of the loops connected to selectively vary the excitation of the additional field winding means.

4. In a control system for a strip of material having a plurality of freely suspended loops, an entry pinch roll motor connected in driving relation with pinch rolls on the entry side of the loop, an intermediate pinch roll motor connected in driving relation with a pair of pinch rolls intermediate the loops, a main generator connected to supply electrical energy to said motors, a delivery pinch roll motor connected in driving relation with pinch rolls on the delivery side of the loops, an additional main generator connected to supply electrical energy to the delivery pinch roll motor, a booster generator connected in series circuit relation with the intermediate pinch roll motor, said booster generator having a plurality of field windings, circuit means connecting two of said windings one to each of the main and additional main generators in opposed senses, and additional field winding means, light sensitive means disposed to be continuously responsive to the difference in the lengths of the loops connected to selectively vary the excitation of the additional field winding means, and additional controlmeans responsive to joint movement of the loops from a predetermined position operable to vary the output voltage of the additional generator to restore the loops to said position.

5. In a control system for maintaining a plurality of loops in a moving length of material at equal and constant lengths, in combination, a plurality of motors connected in driving relation with the length of material at spaced apart points ahead of, between and following a pair of loops in the material, a generator for energizing the motor ahead of the first loo and the motor between the loops, a second generator or energizing the motor beyond the second loop, a booster generator in series with the motor in driving relation with the material between the two loops, a field winding on the booster generator, photothyratron loop regulator means having a continuously variable output connected to control the energization of the field winding in one sense in proportion to the length of the first loop, a second field winding on the booster generator, and photothyratron loop regulator means having a continuously variable output connected to control the energization of the second field winding to act in an opposite sense to the first field winding and in proportion to the length of the second loop, whereby the loops are maintained at equal lengths.

6. in a control system for maintaining a plurality of loops in a moving length of material at equal and constant lengths, in combination, a plurality of motors connected in driving relation with the length of material at spaced apart points ahead of, between and following a pair of loops in the material, a generator for energizing the motor ahead of the first loop and the motor between gizing the motor beyond the second loop, a booster generator in series with the motor indriving relation with the material between the two loops, a field winding on the booster generator, photohyratron loop regulator means having a continuously variable output connected to control the energization of the field winding in one sense in proportion to the length of the first loop, a second field Winding on the booster generator, photothyratron loop regulator means having a continuously variable output connected to control the energization of the second field winding to act in an opposite sense to the first field winding and in proportion to the length of the second loop, whereby the loops are maintained at equal lengths, and means responsive to the second photothyratron loop regulator for varying the voltage of the second generator to thus change the speed of the motor beyond the second loop to maintain the length of the loops constant.

7. In a control system for maintaining a plurality of loops in a moving length of material at equal and constant lengths, in combination, a plurality of motors connected in driving relation with the length of material at spaced apart points ahead of, between and following a pair of loops in the material, a generator for energizing the motor ahead of the first loop and the motor between the loops, a second generator for energizing the motor beyond the second loop, a booster generator in series with the motor in driving relation with the material between the two loops, a field winding on the booster generator, photothyratrdh loop regulator means having a continuously variable output connected to control the energization of the field winding in one sense in proportion to the length of the first loop, a second field winding on the booster generator, photothyratron loop regulator means having a continuously variable output connected to control the energization of the second field winding to act in an opposite sense to the first field winding and in proportion to the length of the second loop, whereby the loops are maintained at equal lengths, a control field winding on the booster gen erator, connected to the first generator, wound to excite the booster in one sense,-a second control field winding on the booster generator, connected to the second generator, wound to act in opposition to the first control field winding.

8. In a control system for maintaining a plurality of loops in a moving length of material at equal and conthe loops, at second generator for enerconnections with the strip at points stant lengths, in combination, a plurality of motors connected in driving relation with the length of ma terial at spaced apart points ahead of, between and following a pair of loops in the material, a generator for energizing the motor ahead of the first loop and the motor between the loops, a second generator for ener gizing the motor beyond the second loop, a booster generator in series with the motor in driving relation with the material between the two loops, at field winding on the booster generator, photothyratron loop regulator means having a continuouslyvariable output connected to control the energization of the field winding in one sense in proportion to the length of the first loop, a second field winding on the booster generator, photothyratron loop regulator means having a continuously variable output connected to control the energization of the second field winding to act in an opposite sense to the first field Winding and in proportion to the length of the second loop, whereby the loops are maintained at equal lengths, and means responsive to the second photothyratron loop regulator for varying the voltage of the second generator to thus change the speed of the motor beyond the second loop to maintain the length of the loops constant, a control field winding on the booster generator, connected to the first generator, wound to excite the booster in one sense, a second control field winding on the booster gen erator, connected to the second generator, wound to act in opposition to the first control field winding.

9. A control system for a plurality of motors connected in driving relation with a strip of material be tween and on, either side of a pair of freely suspended loops in said strip comprising, a first main generator connected to supply electrical energy to the motors connected in driving relation with the material ahead of and between the loops, a second main generator connected to supply electrical energy to the other one of said motors, and a booster generator connected in series circuit relation with the motor connected in driving relation with the material between the loops, said booster generator having opposing field windings enerm'zed in accordance with the voltages of the main generators and connected to maintain the voltage of the motor between the loops at, a value substantially intermediate those of the main generators.

10. In a multiple loop control system, the combination with motors respectively connected in driving relation with a strip of material between and on either side of a pair of freely suspended loops, of a first main generator connected to supply electrical energy to the motor connected in driving relation with the material between and the motor connected in driving relation with the material ahead of the loops, a second main generator connected to supply electrical energy to the other one of the motors, a booster generator connected in circuit relation with said first main generator andthe motor connected in driving relation with the material between the loops, said booster generator having a plurality of field windings, including windings connected in opposed senses for encrgization in accordance with the voltages of the main generators, and circuit means responsive to vary the output voltage of the second main generator in accordance with the lengths of both of the loops.

11. A multiple loop control system for a strip of material disposed to have, a pair of freely suspended loops therein comprising, a plurality of motors having driving between the loops and either ride of the loops, a first main generator eonto aupply electrical energy to the motors connected in driving relation with the material ahead of and between the loops, a reel motor connected in driving relation with a reel device disposed to wind the strip beyond the motor on the trailing side of the loops, a second main generator connected to supply electrical energy to the reel motor and said motor connected in driving relation with the material on the trailing side of the loops, a booster generator connected in series circuit relation with the motor connected in driving relation with the material between the loops having a plurality of field windings including field windings respectively connected in opposed relation to be energized in accordance with the voltages of said main generators,

and circuit means, including photothyratrop loop regulator means, to be variable in accordance with the positions of the respective loops.

References Cited in the tile of this patent UNITED STATES PATENTS 

